Al Gore’s presentation for the Climate Reality Project was broadcast at midnight (GMT) last Thursday, and has garnered a certain amount of attention, particularly in North America.

A lot of the attention has focused on the social and political impacts of the campaign. But with presentations focusing on the “new normal” of increasing extreme weather events around the world, this post takes a look at some of the key claims on the different types of phenomena the Project’s presenters focused on, and what links, if any, scientists have found between these and climate change.

Due to constraints of time and language, we looked at two presentations: Al Gore’s from New York, and John Zavalney’s from Boulder, Colorado. Our assessment is therefore not an in-depth look at the scientific worth of the Climate Reality project – that would take quite a lot longer – but an insight into the scientific merits of two sample presentations.

â?¢ “People are … suffering the effects of the heatwaves” (Gore)

The European heatwave of 2003 was described by a 2008 US Climate Change Science Program report as “far outside the range of historical observations”. A study of the heatwave concluded that:

“…It is very likely (confidence level >90%) that human influence has at least doubled the risk of a heatwave exceeding this threshold magnitude.”

The US Climate Science report says of North America:

“Accompanying a general rise in the average temperature, most of North America is experiencing more unusually hot days and nights. The number of heat waves (extended periods of extremely hot weather) also has been increasing over the past fifty years… Human-induced warming has likely caused much of the average temperature increase in North America over the past fifty years and, consequently, changes in temperature extremes.”

However, scientists studying the Russian heatwave of 2010 attributed it to natural climate variations, although they could not rule out climate change as a cause. Their work did indicate that the likelihood of extreme heatwaves in Russia will increase in the next few decades as greenhouse gases rise.

â?¢ “Longer and deeper droughts… killing crops and animals and people, driving up food prices and causing people to leave communities that they have called home for many generations…” (Gore)

A paper reviewing the link between drought and global warming ascribes drought to regions drying, the drying to temperature increases, and temperature increases in large part to human-generated greenhouse gases:

“Since the middle 20th century, global aridity and drought areas have increased substantially, mainly due to widespread drying… Since a large part of the recent warming is attributed to human-induced GHG [greenhouse gas] increases, it can be concluded that human activities have contributed significantly to the recent drying trend.”

The World Food Programme state that:

“Drought is now the single most common cause of food shortages in the world. In 2006, recurrent drought caused crop failures and heavy livestock losses in parts of Ethiopia, Somalia and Kenya.”

Stated estimates for deaths due to drought differ quite widely. UNESCO reports that droughts caused 280,000 deaths between 1991 and 2000, whilst the Centre for Research on the Epidemiology of Disasters suggests that droughts killed around 20,000 people per year between 1980 and 2008 – 558,000 in total. The UN Food and Agriculture Organisation puts the number of deaths substantially higher, estimating that droughts displaced 10 million farmers were displaced during the 1980s and that 1 million died.

“Droughts in Africa during the 1980s forced 10 million farmers to abandon their land; over 1 million died.”

As Anna Mazhirov of the Columbia University Climate Center noted in March, there is a direct link between the increasing incidence of drought globally and rising food prices:

“Between 2006 and 2008, world average prices rose by 217 percent for rice, 136 percent for wheat, 125 percent for corn, and 107 percent for soybeans. Droughts in grain-producing regions were a leading cause for this world food price crisis, which led to food riots and political change.”

â?¢ “fires … spreading wildly and burning hotter and more intensely and burning longer …” (Gore)
â?¢ “fires are … spreading wildly, and burning hotter, longer and bigger” (Zavalney)

A 2004 Geophysical Research Letters paper found that:

“…Human-induced climate change has had a detectable influence on the area burned by forest fire in Canada over recent decades.”

Whilst a 2006 Nature paper found that:

The EPA report “Climate Change Indicators in the United States” notes that:

As the US Climate Change Science Program concludes,

As a recent Nature paper found:

This is supported by Kevin Trenberth’s Climate Research paper which highlights a clear link between extremes in rainfall and rising temperatures, finding that “extreme flooding has increased in the 20th century”. The study notes that estimates for world flood damage reach billions of US dollars, and that thousands of lives have been lost thanks to extreme rainfall events.

A 2008 Nature paper found that strong tropical storms are becoming stronger, concluding:

As Nature noted in an accompanying piece, this study found

The US Climate Change Science Program’s 2008 report on extreme weather and climate change notes that

A recent Science paper finds that wind speeds increased globally between 1985 and 2008. However the study is unable to draw conclusions about links with climate change as the data used only covers two decades, not long enough to separate acceleration from multi-decadal natural variation.

Our ability to attribute observed trends has also been disputed in other papers. A 2010 Nature paper for instance, draws attention to the difficulties in making attributions:

A recent Climate Science Rapid Response Team briefing paper on severe thunderstorms and tornadoes is also circumspect. It concludes that while “[l]arge-scale climate change is also likely to affect small-scale phenomena like severe thunderstorms and tornadoes”, the “nature and the degree of influence are very uncertain”.

With regard to storms’ “destructiveness”, calculations of damages are also seen as inconclusive by some scientists. A 2011 Bulletin of the American Meteorological Society paper found that 22 studies demonstrated that weather-related natural hazards including storms and cyclones have increased economic losses around the world. However, this could not be attributed to manmade climate change.

Another paper states that:

“[r]ecent reviews have concluded that efforts to date have yet to detect or attribute an anthropogenic climate change influence on Atlantic tropical cyclone (of at least tropical storm strength) behaviour and concomitant damage.”